The mean scale score on the mathematics examinatin of ninth graders in Texas was 86 with a standard deviation of 5 points. Given a student was selected at random what is the probability that his score was 91 or higher
Use z-scores:
z = (91 - 86)/5 = ?
Once you calculate the z-score, check a z-table for the probability. (Remember that the problem is asking what is the probability the score was 91 or higher.)